1. Field of the Invention
This invention relates generally to integrated circuits and more particularly to high speed direct connection between integrated circuits.
2. Description of the Related Art
In electronic devices such as personal computers, an integrated circuit such as the microprocessor, typically communicates with other integrated circuits via buses, which are formed physically as traces in a printed circuit board (PCB). Most integrated circuits (ICs) are packaged in plastic or ceramic packages or are otherwise encapsulated to protect the device. Pins or other contacts connect the package to the printed circuit board. There are a wide variety of packages and packaging techniques used for integrated circuits including dual inline packages (DIP), pin grid array (PGA) packages, land grid array (LGA) packages, and ball grid array (BGA) packages. DIPs provide two rows of connectors on the periphery of the package. PGA packages provide an array of pins on the bottom surface of the package. The LGA package provides an array of lands while the BGA package uses an array of solder balls or bumps as the electrical contacts. Chip scale packages are similar to BGA packages, except that chip scale packaging provides a smaller footprint that more closely approximates the footprint of the semiconductor die itself.
The electrical contacts on the various packages may be soldered directly to the printed circuit board or otherwise coupled to the PCB through, e.g., an intermediate device such as a socket. For example, a pin grid array package with a mounted IC die has pins projecting from the package that can be inserted in a zero insertion force (ZIF) socket, which itself is mounted on the printed circuit board. Utilizing sockets such as ZIF sockets allows for the integrated circuit to be easily inserted and removed.
In personal computer (PC) systems, the processor is commonly mounted in a socket that is itself soldered to the PCB. In a typical PC system, the processor and its associated chipset are packaged in separate plastic or ceramic packages and are interconnected through the motherboard or another printed circuit board such as a daughter card. The processor in typical PC configurations communicates with one chip of a chipset (known as the northbridge in the industry) that supports the microprocessor. The northbridge provides memory control as well as system bus control for the computer system and communicates with the processor over a local bus. As clock speeds have increased for the processor, now commonly over 1 GHz, bus speed for the local bus (and other buses) and have also increased. The noise and impedance effects that result from routing a bus through the printed circuit board are to particularly acute for high speed buses, especially where relatively long traces (e.g., over three inches) have to be used for the communication path.
Multi-chip module (MCM) technology can be used where speed or electrical noise considerations require a shorter communication path or applications where it is necessary to minimize size such as in a mobile device. A typical MCM package combines a number of individual integrated circuit dies, which are attached to a mounting surface such as a ceramic substrate. The integrated circuits within an MCM can be electrically connected using a variety of bonding techniques such as solder, wire bonding, tape automated bonding (TAB), and flip-chip technologies. Thus, MCMs can provide an alternative to routing high speed connections on a printed circuit board such as a motherboard of a computer system. However, such MCM technology is costly and therefore undesirable for applications such as desktop personal computers.
Accordingly, it would be desirable to provide high speed connections between ICs without having to route the communication path through the PCB and without having to resort to a relatively costly MCM solution.
Accordingly, in one embodiment the invention provides an apparatus that includes a first integrated circuit mounted in a first package that has both a first set of electrical contacts and a first connector. A second integrated circuit is mounted in a second package that has a second set of electrical contacts and a second connector. The first and the second connectors are mating connectors that are electrically and physically connected.
In one embodiment the first set of electrical contacts and the first connector are disposed on opposite surfaces of the first package and the second set of electrical contacts and the second connector are disposed on the same surface of the second package. Providing the connectors allows higher speed signals to be routed through the first and second connectors, while power, ground and slower speed signals can be transmitted through the first set and second set of electrical contacts. The first and second set of electrical contacts are on the side of the package closest to the printed circuit board to which the packages are directly or indirectly mounted.
In another embodiment a method is provided that includes electrically coupling a first integrated circuit mounted in a first package through a first set of electrical connectors to a printed circuit board; and electrically connecting the first integrated circuit through a first package connector to a second integrated circuit mounted in a second package having a second package connector, wherein the first and second package connectors are mating connectors.